Fire detector stabilizer circuit

ABSTRACT

A fire detector has been provided including an ionization sensing means which changes the level of an output signal in accordance with the sensing of the presence of smoke particles in the atmosphere. A detecting means including a semi-conductor device selectively responds to the output signal and generates an alarm control signal. The improvement includes a very high frequency pump source coupled across the sensing and detecting means for stabilizing the ionization and to quench areas of intense ionization within the sensing means and the semiconductor.

Elnited States Patent Burnett 1 Apr. 17,1973

1541 FIRE DETECTOR STABILIZER 3,530,450 9/1970 Walthard et al ..340 237s CIRCUIT 3,018,376 1/1962 Vanderschmidt ..250/43.5 D x [75] Inventor:James H. Burnett, Wilton, Conn. Primary Examiner john W- Caldwell [73]Assignee: Edward Company, Inc., Norwalk, Assislant x i -D ni l Myer cAttorney-Harold S. Wynn and John P. DeLuca [2] 1 Appl' 79972 A firedetector has been provided including an ionization sensing means whichchanges the level of an out- 52 us. c1. ..340/237 5, 250/83.6 FT PutSignal in accordance with the sensing of the 51 Int. Cl. ..G08b 17/10,1101 j 39/28 Wm"Ce Smke Particles in atmsphere- A 58 Field of Search..340/237 swing means including a semi'wnducmr device 250/43 5 D 44 83 6selectively responds to the output signal and generates an alarm controlsignal. The improvement includes a [56] References Cited very highfrequency pump source coupled across the sensing and detecting means forstabilizing the ioniza- UNITED STATES PATENTS tion and to quench areasof intense ionization within the sensing means and the semi-conductor.3,295,121 12/1966 Meyer ..340/237 S 3,160,866 12/1964 Meili ..340/237 S9 Claims, 1 Drawing Figure R j'( MN 1 I R C F. ET. TRIGGER so R. ALARM I7 13 V 14 7 15 10 11 MC 1 E FIRE DETECTOR STABILIZER CIRCUIT BACKGROUNDOF INVENTION The invention relates to smoke detector devices and inparticular to apparatus for stabilizing and increasing the sensitivityof such devices.

Ionization sensing devices as used in the present in vention requiresthe imposition of an electric field across electrodes within. Ionparticles are emitted by a radioactive source and the electric fieldfacilitates a flow of current through the sensing chamber essential tothe operation of such devices. The configuration of the field intensitythroughout the chamber may not necessarily be uniform which detractsfrom the efficient operation of the device as a smoke detector, and assuch, careful manipulation of electrode geometry is often required tomaximize the effects of aerosols within the chamber.

Another problem arises with respect to the strength of the radio-activesource. It is generally required that the source be rather weak in orderto avoid the affects of radiation on personnel. A weak source, however,may decrease the efficiency of the detector, and limit its utility tocertain applications.

Use of semi-conductors as one of the more recent developments in thefire detector art has added the convenience and economy of low voltagepower supplies. These devices because of the nature of semi-conductorsare able to produce a signal indicative of a smoke or fire conditionwithout expensive and sometimes cumbersome electronic tube devices.There have arisen, however, problems associated with stability of thesemi-conductor devices, some types of which have exhibited erraticbehavior in the environments wherein they are utilized. Impurities orflaws in the semi-conductors, in many cases, make reliable detectionssometimes very difficult. Without elaborate sensitivity compensation,these devices may be erratic in their behavior and sense anything froman actual fire to a draft in the room or area to be supervised. Inaddition, fluctuation of ambient conditions may add to the problem ofaccurate detection.

It is therefore an object-of the present invention to provide anarrangement which substantially obviates one or more of the limitationsof the described prior art arrangements.

It is another object of the present invention to provide a system whichis more stable under varying conditions to which it is subjected.

It is yet another object of the present invention to provide a firedetector system which is stable, sensitive and economically implemented.

SUMMARY OF INVENTION There has been provided a fire detector includingan ionization sensing means for changing the level of an output signalin accordance with sensing the presence of smoke in the atmosphere and adetecting means which includes a semi-conductor device selectivelyresponsive to the output signal for generating an alarm control signal.The improvement comprises means including a very high frequency sourcecoupled across the sensing and detecting means for stabilizingionization and for quenching areas of intense ionization within thesensing means and the semi-conductor.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, while itsscope will be pointed out in the appended claims.

The drawing is a block diagram of the apparatus forming one embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus of the presentinvention includes a smoke sensing device 1 1 having two ionization typedetectors. The general type of detector contemplated for use in thisdevice can be seen in a patent by Abe, U.S. Pat. No. 3,500,368. Thatdevice includes two ionization chambers; one substantially open to theatmosphere for detecting ionization products of smoke and the other areference chamber which is substantially isolated from smoke particlesbut contains atmosphere for compensating changes in the ambientatmospheric pressure. The chambers shown in the drawing in the presentdisclosure include a reference chamber RC which establishes a referencepotential and is substantially isolated from the combustion products inthe atmosphere and a measuring chamber MC connected in series therewithwhich changes the potential at the junction of the two chambers upon thevariations in concentration of the aerosols in the atmosphere. Thechambers RC and MC are coupled across an electrical potential and eachchamber has disposed therein a relatively weak source of radio-activematerial for ionizing the atmosphere within each of the chambers, suchthat under the influence of the potential, a current flows through thechambers. When atmospheric aerosols enter the measuring chamber MC, thecurrent is decreased because the ionized particles produced by theradio-active source combine with the smoke particles thus reducing thetotal net movement of charge within the measuring chamber MC.Consequently, the potential across electrodes disposed in the measuringchamber MC increases and changes the potential of the junction betweenthe two chambers RC and MC. This potential is coupled directly to aninput of field effect transistor 12. This transistor 12 can have itselements connected as disclosed in the above mentioned Abe U.S. Pat. No.3,500,368. A field effect transistor was chosen because the inputimpedance of such a device is extremely high and does not load theseries circuit consisting of the chambers RC and MC in sensing means 11.This is important because the current flowing through the chambers isextremely limited and such loading would adversely affect the operationof the detector. If the potential at the junction between the chambersRC and MC changes by a predetermined amount established by the biasingof the FET 12, it becomes conductive and produces a signal to trigger acircuit 13. This circuit 13 acts somewhat as a buffer between the PET 12and an output control circuit 14 including a silicon controlledrectifier which activates,

therefore improper conduction. Even in the case of a very high qualitysemi-conductor device, the procedure set forth below has been found tobe very useful in improving what has heretofore been rather asatisfactory operation.

Improvement to the system as contemplated by the present invention, isaccomplished by imposing a very high A.C. pump frequency across thefield effect transistor 12 which has been found to quench the ionizationof impurities in the semi-conductor. An A.C. pump is coupled across thesensing means 11, FET 12 through coupling capacitors C and resistors R.The R-C combinations are tuned to the pump 10 frequency and high qualitycomponents are chosen to yield a very high Q or quality factor at thepump frequency. The capacitive effect of the electrodes within thechambers RC and MC and the junction capacitance of the FET 12 is takeninto consideration to further precisely tune the coupling circuit to thefrequency of the pump 10. The current generated by the pump 10 isprimarily coupled across the chambers RC and MC, while resistors R limitthe current to the remainder of the circuit including the FET 12. Theamplitude of the A.C. signal produced by the pump 10 is substantiallyequal to or slightly higher than the bias placed across the chambers RCand MC by the source potential shown in the drawing as and Theimposition of the low level A.C. signal substantially eliminatesnon-uniform ionization occurring within the chambers RC and MC and PET12 at the local flaws. The trigger circuit 13 and the SCR circuit 14,include semi-conductor devices and the presence of the A.C. pump 10substantially improves their operating characteristics also. However, itis primarily the focus of the invention to increase the sensitivity ofthe chambers RC and MC and prevent erratic operation of the FET 12 sinceit is required to detect the low level signal change at the junction ofthe chambers RC and MC. The ionization characteristics of the chambersRC and MC and the response of PET l2 tend to be more uniform inoperation and the latter more sensitive to the changes in the potentialat the junction of the two chambers. Thus, the system is more efficientin its initiating the signals for activating the alarm 15.

The imposition of the relatively high A.C. pump 10 frequency alsoincreases many fold the ionization characteristics of the radio-activesource. The sensitivity of the device was noted to increase by at leasta factor of 10 by the imposition of a 10 MHz signal, and further as thefrequency was increased. It is therefore possible to reduce theradiation level substantially to a nominal value by increasing thefrequency of the pump 10.

There has therefore been provided an improved fire detector whichincorporates a very high frequency alternating current pump whichquenches intense ionization within the semi-conductor device andprovides a stabilizing effect to the semi-conductor as well.

While there has been provided what is at present is the preferredembodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the true spirit and scope of the invention, and it isintended in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A fire detector stabilizer circuit comprising in combination:

a. a smoke sensing device having an ionization detector for changing theoutput level of a signal in response to the presence of smoke in theatmosphere;

b. detecting means including a semi-conductor device which isselectively responsive to the output level of said smoke sensing devicefor generating an alarm control signal;

c. a DC potential for inducing a current flow in said smoke sensingdevice;

. a very high frequency source including an alternating current pumpcoupled across said smoke sensing device and said detecting means forquenching non-uniform ionization of said smoke sensing device; andwherein e. said alternating current pump produces a radio frequencysignal at a voltage level substantially equal to, or slightly higherthan, that of said DC potential and less than the bias level of saidsemiconductor.

2. The apparatus of claim 1 wherein said very high frequency source iscoupled to the fire detector, by coupling means tuned to the frequencyof the alternating current pump.

3. The apparatus of claim 2 wherein said semi-conductor is a fieldeffect transistor having:

a. a voltage level sensitive gate electrode coupled to the smoke sensingdevice and;

b. output terminals coupled to the output of said alternating currentpump; and wherein c. said field effect transistor achieves a conductancestate in response to a predetermined variation of the voltage level ofsaid gate electrode.

4. The apparatus of claim 3 wherein said smoke sensing device includes:two chambers including electrodes having the ionization potentialimposed thereon serially coupled across the alternating current pump andhaving their junction coupled to the gate of said field effecttransistor.

5. The apparatus of claim 2 wherein said coupling means includes:resistive and capacitive impedances for tuning the coupling means andsaid capacitive impedance further comprises inter-electrode capacitiveeffects of said chambers and junction capacitive effects of saidsemi-conductor.

6. The apparatus of claim 5 wherein said chambers comprise: a referencechamber substantially isolated from the smoke for establishing areference potential; and a measuring chamber open to the atmosphere forproducing a change in the potential at the junction of the chamber inaccordance with the concentration 0 smoke in the atmosphere.

7. The apparatus of claim 4 wherein said detector further includes:output circuit means responsive to the conductance state of said fieldeffect transistor for producing the alarm control signal.

8. The apparatus of claim 7 wherein said output circuit includes: atrigger circuit responsive to the conductance state of the field effecttransistor for producing an output; and a control rectifier having agate electrode coupled to the output of said trigger circuit assuming aconductance state upon the occurrence of the trigger output forproducing said alarm control signal.

9. The apparatus of claim 8 wherein said trigger means and said controlrectifier means include semiconductor devices coupled therein, and saidoutput circuit means is coupled across said alternating current pumpoutput for further stabilizing the response of said 5 semi-conductordevices.

1. A fire detector stabilizer circuit comprising in combination: a. asmoke sensing device having an ionization detector for changing theoutput level of a signal in response to the presence of smoke in theatmosphere; b. detecting means including a semi-conductor device whichis selectively responsive to the output level of said smoke sensingdevice for generating an alarm control signal; c. a DC potential forinducing a current flow in said smoke sensing device; d. a very highfrequency source including an alternating current pump coupled acrosssaid smoke sensing device and said detecting means for quenchingnon-uniform ionization of said smoke sensing device; and wherein e. saidalternating current pump produces a radio frequency signal at a voltagelevel substantially equal to, or slightly higher than, that of said DCpotential and less than the bias level of said semi-conductor.
 2. TheApparatus of claim 1 wherein said very high frequency source is coupledto the fire detector, by coupling means tuned to the frequency of thealternating current pump.
 3. The apparatus of claim 2 wherein saidsemi-conductor is a field effect transistor having: a. a voltage levelsensitive gate electrode coupled to the smoke sensing device and; b.output terminals coupled to the output of said alternating current pump;and wherein c. said field effect transistor achieves a conductance statein response to a predetermined variation of the voltage level of saidgate electrode.
 4. The apparatus of claim 3 wherein said smoke sensingdevice includes: two chambers including electrodes having the ionizationpotential imposed thereon serially coupled across the alternatingcurrent pump and having their junction coupled to the gate of said fieldeffect transistor.
 5. The apparatus of claim 2 wherein said couplingmeans includes: resistive and capacitive impedances for tuning thecoupling means and said capacitive impedance further comprisesinter-electrode capacitive effects of said chambers and junctioncapacitive effects of said semi-conductor.
 6. The apparatus of claim 5wherein said chambers comprise: a reference chamber substantiallyisolated from the smoke for establishing a reference potential; and ameasuring chamber open to the atmosphere for producing a change in thepotential at the junction of the chamber in accordance with theconcentration of smoke in the atmosphere.
 7. The apparatus of claim 4wherein said detector further includes: output circuit means responsiveto the conductance state of said field effect transistor for producingthe alarm control signal.
 8. The apparatus of claim 7 wherein saidoutput circuit includes: a trigger circuit responsive to the conductancestate of the field effect transistor for producing an output; and acontrol rectifier having a gate electrode coupled to the output of saidtrigger circuit assuming a conductance state upon the occurrence of thetrigger output for producing said alarm control signal.
 9. The apparatusof claim 8 wherein said trigger means and said control rectifier meansinclude semi-conductor devices coupled therein, and said output circuitmeans is coupled across said alternating current pump output for furtherstabilizing the response of said semi-conductor devices.